Add @independent_variables macro (just passes through @parameters, for now)

Author: hersle

src/ModelingToolkit.jl

@@ -127,6 +127,7 @@ using .BipartiteGraphs
 
 include("variables.jl")
 include("parameters.jl")
+include("independent_variables.jl")
 include("constants.jl")
 
 include("utils.jl")
@@ -262,7 +263,7 @@ export generate_initializesystem
 export alg_equations, diff_equations, has_alg_equations, has_diff_equations
 export get_alg_eqs, get_diff_eqs, has_alg_eqs, has_diff_eqs
 
-export @variables, @parameters, @constants, @brownian
+export @variables, @parameters, @independent_variables, @constants, @brownian
 export @named, @nonamespace, @namespace, extend, compose, complete
 export debug_system
 

src/independent_variables.jl

@@ -0,0 +1,11 @@
+"""
+    @independent_variables t₁ t₂ ...
+
+Define one or more independent variables. For example:
+
+    @independent_variables t
+    @variables x(t)
+"""
+macro independent_variables(ts...)
+    :(@parameters $(ts...)) |> esc # TODO: treat independent variables separately from variables and parameters
+end